A9 upgrade

However, he said shorter journey times and other upgrades should be made.

The A9 dualling is a colossal road engineering project and with that comes detailed planningScottish government spokesman

A Scottish government spokesman said: "We are taking every possible step to dual the A9 between Perth and Inverness as quickly and efficiently as possible."

He added: "The A9 dualling is a colossal road engineering project and with that comes detailed planning to ensure we deliver a road that meets the aspirations of all the communities and road users along its length.

"The Scottish government agrees with CBI Scotland that it is absolutely vital that access to Heathrow is secured for Scottish flights and the loss of an Inverness-Heathrow connection was undoubtedly a blow to the Highland economy."

He added that work on the Caledonian Sleeper franchise, and investment of more than £100m, was intended to give the historic service the "21st Century future" it deserved.

In June last year, the Scottish government said a £3bn programme of work to make the A9 dual carriageway all the way from Inverness to Perth would start early.

The improvements will begin by 2015-16, rather than 2017-18, with an enhancement of the Kincraig to Dalraddy overtaking lane south of Aviemore.

The full project is not expected to be completed until 2025.

There are about 80 miles (128.7km) of single carriageway between the cities.